1. Field of the Invention
This invention relates to a communications system and to a method of controlling the same.
2. Description of the Related Art
A system connected to a communications network to perform communication is so adapted that the user selects the communications network in advance to carry out communication. The selection is made in conformity with the transmission quality requirement necessitated by the type of data handled by the system. Examples of networks that can be selected are a PSTN (Public Switched Telephone Network), ISDN (Integrated Services Digital Network), PSPDN (Packet Switching Public Data Network) and the Internet.
By way of example, a system requiring little delay as in the case of a videoconference system is connected to a PSTN or ISDN, whereas a system that allows some delay, such as a system for data transfer and e-mail, is connected to a PSPDN or the Internet.
However, in a case where a system that employs a coding/compression scheme conforming to the connected communications network to perform voice/image communication by a protocol related to the TCP/IP (Transmission Control Protocol/Internet Protocol) is configured for a network such as a PSTN, ISDN or Internet, the prior art described above is such that the network to which the connection is to be established must be decided beforehand and the related settings must be made. For example, there are cases where it is desired to perform long-distance communication via the Internet and short-distance communication via an ISDN. In such cases, communication terminal settings must be changed by manual input whenever communication is performed. There are also cases where it is desired to transmit by a PSTN line, even for short-distance communication, because an ISDN line is busy. And there are instances where it is desired to communicate directly via an ISDN line because of heavy traffic congestion on the Internet and an inability to obtain satisfactory quality for communication owing to the time delay. In all of these cases the operator must change the connections and data settings each time. This is a very troublesome task.
More generally, with a system of the type that is connected to a network, typified by an ATM network, in which it is usually possible to reserve the resources that satisfy the required communications quality, what can and cannot be communicated upon relaxing the quality requirement must be selected if resources that will make it possible to obtain the sought communications quality cannot be reserved. Even achieving the downgrading of the communications quality requirement demands that the operator change the requirement manually. There are many quality-related items, such as delay, loss and bandwidth, and the operator must decide which item is to undergo the reduction in quality and in what way. However, the prior art is such that such instances cannot be dealt with in a flexible manner.
An object of the present invention is to provide a communications system in which the communications quality of a system can be changed in appropriate fashion in dependence upon the status of a network.
Another object of the present invention is to make it possible to change a communications quality requirement automatically.
Another object of the present invention is to select an optimum route based upon a changed communications quality requirement.
A further object of the present invention is to assign priorities to communications qualities.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.